Magmatism along the high Paraguay River at the border of Brazil and Paraguay: A review and new constraints on emplacement ages

Comin-Chiaramonti, P., Gomes, C.B., De Min, A., Ernesto, M. and Gasparon, M. (2015) Magmatism along the high Paraguay River at the border of Brazil and Paraguay: A review and new constraints on emplacement ages. Journal of South American Earth Sciences, 5872-81. doi:10.1016/j.jsames.2014.12.010

The magmatic rocks from Alto Paraguay (High Paraguay River extensional lineament), western Apa craton, mainly consist of several major circular alkaline complexes and some rhyolitic domes and ignimbrites. The former are characterized by intrusive Na–alkaline rock-types (nepheline syenites and syenites and effusive equivalents) topped by lava flows and ignimbrites. Two main evolved suites were defined using petrochemical and Sr– isotope data: an agpaitic suite in the north and a miaskitic suite in the south. The domes of subalkaline rhyolitic lavas and ignimbrites occur to the north of the alkaline complexes, along the Paraguay River, near the town of Fuerte Olimpo.

Rb–Sr systematics (87Sr/86Sr initial ratios ≤ 0.7038) highlight a relatively “primitive” character of the Na–alkaline magmatic source(s), in contrast with the “crustal” values (87Sr/86Sr initial ratio ∼ 0.7105) of the Fuerte Olimpo rhyolites. Thus, magmatism in the Alto Paraguay area is related to two extensional events: a younger event corresponding to the Permian–Triassic alkaline rocks, and an older event connected to the Precambrian volcanic acidic rocks.